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ERROR_INVALID_IMPORT_OF_NON_DLL
The DLL imports from a module type the loader cannot use.
ERROR_INVALID_IMPORT_OF_NON_DLL is Win32 error 1276 (0x4FC). A DLL’s Portable Executable import metadata references a module that is not a DLL and is not the process executable image. The loader rejects the dependency relationship before the importing component can initialize.
How the invalid import can be created
- a build step links against an import library generated from the wrong image
- a file named like a DLL actually contains an EXE or another unsupported format
- post-build rewriting corrupts or replaces an import descriptor
- a packaging collision deploys an executable over the expected DLL path
- architecture-specific outputs are mixed and dependency selection reaches the wrong file
Evidence to preserve
Record the importing image, full path of the referenced module, process architecture, file hash, PE machine type, image characteristics, import table entry, and loader search path. Capture loader snaps or debugger output showing which physical file satisfied the module name. A directory listing alone is insufficient because the wrong file may carry the expected name.
Diagnostic sequence
Inspect the importing DLL’s import directory with a PE-aware tool and identify the offending module name. Open the resolved target’s PE headers and verify its image type and machine architecture. Compare the deployed files with build artifacts and package manifests, then inspect how the import library was produced.
Check search-order effects and side-by-side copies. A valid DLL in the application directory does not help if an earlier search location or explicit path selects a non-DLL image. Also verify that installers and update rollback do not rename EXE and DLL outputs into a shared destination.
Recovery
Deploy the correct DLL or rebuild the importing image against the proper import library. Remove the packaging collision and validate hashes before retrying in a fresh process. Do not rename an executable to .dll; the file extension does not change PE image characteristics or make its export/import contract valid.
Difference from nearby loader errors
ERROR_INVALID_DLL broadly says a required library is damaged. ERROR_BAD_EXE_FORMAT covers invalid or incompatible image format. ERROR_DLL_INIT_FAILED occurs after loading reaches initialization. Error 1276 specifically identifies an import that targets a non-DLL module.
Example
A build pipeline generates tools.exe and tools.dll, but a packaging rule copies the EXE to both destination names. A plug-in DLL imports functions from tools.dll; the loader resolves that path to the mislabeled executable and returns 1276. Correcting the package manifest fixes the startup failure.
References
- Microsoft: System Error Codes (1000–1299)
- Microsoft: PE Format
- Microsoft: IMAGE_DATA_DIRECTORY structure
- Microsoft: Dynamic-Link Library Search Order
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